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Flashcards in Meteorology Deck (78)
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1
Q

How is wind described?

A

Wind direction- the direction FROM WHICH the wind is blowing, expressed in terms of degrees clockwise from north.
Wind strength- expressed in knots (kts).

Direction and strength combined give VELOCITY.

If the wind direction INCREASES it is said to be VEERING, if the wind direction DECREASES it is said to be BACKING.

2
Q

What causes the wind to blow?

A

Pressure Gradient Force- movement of air from a high pressure area to a low pressure area.
Coriolis Force- (not actually a force!), apparent change in direction caused by the earth’s rotation. Alters the direction of movement to the RIGHT in the northern hemisphere.

3
Q

What is a Geostrophic wind?

A

The wind produced by the effect of the Coriolis force on a Pressure Gradient wind. Wind is bent to the right until it follows the line of the pressure isobars.

Therefore Gradient winds blow anti-clockwise around low pressure areas and clockwise around high pressure areas.

Buys Ballot’s Law- If you stand with your back to the wind in the Northern Hemisphere, the lower pressure is always toner left.

4
Q

What are the effects of friction on Surface Wind over the land and sea?

A

Over Sea- Wind will BACK by approximately 10° and its speed will be reduced to 80% of Geostrophic wind speed.
Over Land- Wind will BACK by approximately 20° and its speed will be reduced to 40% of Geostrophic wind speed.

5
Q

What effect does surface wind have on aircraft operations at aerodromes?

A
  • Aircraft take off and land into the wind (more lift, slower for landing). This is the greatest influence for runway selection.
  • Strong winds, sudden changes in wind velocity are hazardous to aircraft.
6
Q

What is a ‘Gust’ of wind?

A

A temporary increase in the mean wind speed lasting a few seconds (associated with turbulent eddies in the friction layer).

7
Q

What is a Mesoscale System?

A

Mesoscale meteorology is the study of weather systems with horizontal dimensions generally ranging from 2-2000km. Eg. sea and land breezes, mountain and valley winds.

8
Q

What are Sea and Land Breezes?

A

Sea breeze- a surface wind which blows from the sea to the land as a result of differential heating of the surface (during the day the land warms faster). They are strongest on a sunny day with a weak pressure gradient.

Land breeze- at night the process may be reversed as the land cools quicker.

9
Q

Describe the 3 types of valley wind.

A

Katabatic wind- at night the land cools quickly, which cools the air making it less dense and causing it to ‘fall’ down the hill.
Anabatic wind- by day the land warms quickly, as the air is warmed it becomes less dense and rises up the hill.
Föhn wind- a dry wind that blows down the lee side of a mountain. Due to the difference in value of the Dry Adiabatic Lapse Rate (DALR) 3°/1000ft, and the Saturated Adiabatic Lapse Rate (SALR) 1.5°/1000ft.

10
Q

What is a tornado?

A

A violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud.
Most tornados have wind speeds less than 110 mph, are approximately 80m across and travel only a few miles before dissipating.

11
Q

What is a waterspout and why might it be dangerous to aviation?

A

Waterspouts are characterised by a spiralling funnel-shaped wind current, connecting to a large cumulus or cumulonimbus cloud. They are generally classified as non-super cellular tornados that develop over bodies of water.

Aircraft flying over the sea or large bodies of water would have to be careful not to get close to one as they are very dangerous.

12
Q

What is wind?

A

The flow of air over the earths surface. Almost completely horizontal- only 1/1000th flow is vertical. This flow is very important to weather and aviation.

13
Q

What is Air Mass?

A

An air mass is a body or mass of air in which the horizontal gradients or changes in temperature and humidity are relatively slight. May cover several million square kms.

14
Q

What are the main weather ‘bands’ of the Earth?

A

InterTropical Convergence Zone (ITCZ):
Permanent Low Pressure belt approximately 10° wide, located near the equator but moves with the seasons between 20°N and 20°S between July and January.

Hadley Cell:
Between the Equator and 30°N/S. Warm air rising near the equator moves pole-ward in the upper troposphere, while cooling air around 30° moves equator-ward at lower levels.

Mid-Latitude Cell (Ferrel Cell):
As air descends at 30° it becomes compressed and denser and creates a High Pressure Belt in the subtropics.

Polar Front:
The boundary between polar air and warmer air is a polar front. The movement of warm air pole-ward and cold air equator-ward is achieved by air moving horizontally. There is a sharp temperature gradient.

Polar Cell:
Within 30 degrees of the Polar cap the air circulation is primarily away from the poles at low levels and towards the poles at upper levels.

The area between the cells has the greatest temperature changes. As the temperature difference increase the wind also increases in the upper atmosphere. Jetstreams can vary in level from 4 to 8 miles and have wind speeds of up to 275mph.

15
Q

What characteristics of the earths surface modify air masses, and how?

A
Air mass moves over:
Ocean surface- becomes more moist at low levels from oceanic evaporation. 
Land/continental area- remains dry.
Warm surface- warms
Cold surface- cools.
16
Q

How do we classify air masses?

A

By region of origin:
- Arctic A. - Antarctic AA. - Polar P. - Tropical T. - Equatorial E.

And by route followed by the air mass:
- Continental c. - Maritime m

17
Q

What are the main Isobaric Features?

A

An area of high pressure is known as an anticyclone.
An area of low pressure is know as a cyclone.
A front is a distinct division between adjacent air masses.
Frontal activity describes the interaction between the air masses as one replaces another.

18
Q

What is a Front?

A

A boundary between two air masses. Shown on a weather map as a line. Has a sloping surface.
Fronts always lie in troughs of low pressure, where pressure decreases and then increases. This is often accompanied by a significant change in the wind direction.

19
Q

What are the characteristics of cold and warm fronts?

A

Cold Front:

  • Steep slope (1:50)
  • Pressure increases as front moves through
  • Temperature decreases as front moves through
  • Wind veers.
  • Often causes Cb or TCu as warm air is forced up, cools and water condenses.
  • High visibility

Warm Front:

  • Shallow slope (1:200)
  • Temperature increases and pressure decreases as front moves through.
  • Wind backs slightly and then veers.
  • Cirrostratus, alto stratus and stratocumulus clouds formed over long distance as warm air creeps slowly higher.
20
Q

What is an Occluded Front?

A

An occluded front occurs when a cold front catches a warm front.
Either the warm air will be forced very high as the colder air then catches the cool air of the preceding high pressure (cold occluded front), or if the preceding cold air is colder than the cold front, both the warm and cold front will be forced higher (warm occluded front).

21
Q

What is a warm sector?

A

The area between a fast moving cold front and preceding warm front, before the warm front is caught.

22
Q

What shall a pilot do on meeting hazardous conditions?

A

On meeting hazardous conditions in the course of a flight the commander shall inform the appropriate ATCU as soon as possible by the quickest means possible, giving particulars of the hazard as may be pertinent to the safety of other aircraft.

23
Q

What conditions are necessary for the formation of thunderstorms?

A
  • Deep instability, eg warm air in lower levels and cold air in upper levels.
  • High moisture content.
  • A trigger action to start the air rising, such as a front forcing the air aloft, mountainous terrain, or strong surface heating.
24
Q

What are the hazards of a thunderstorm for aircraft?

A
  • Severe turbulence
  • Severe icing (large supercooled droplets striking a sub-zero surface)
  • Hail (structural damage)
  • Lightning Strikes
  • Interference to radio communication and radio navigation instruments.
  • Severe wind shear
  • Low cloud base and reduced visibility.
25
Q

What is a Line Squall?

A

A cold front forcing warm air up to create towering Cb over a long lateral distance.

26
Q

How can temperature affect aeronautical activities? (3)

A

High temperature= Low density: reduces aircraft performance so longer take off run needed.
Temperature= Dew Point= Fog: probable holding and low vis procedures.
Very low temperature= Icing: affects control surfaces, de-icing needed before take off.

27
Q

What are the hazards of icing?

A
  • Adverse aerodynamic effects= loss of lift, increase in drag, unbalance of propeller.
  • Piston engine degradation from carburettor icing.
  • Faulty readings from instruments caused by ice blocking pitot tube/static vent.
  • Windscreens frozen.
  • Landing gear accretion- unable to deploy.
28
Q

What should an ATCO he briefed on prior to taking over watch?

A

Controllers shall obtain full information regarding the weather expected during the period of their watch by the study of forecasts, charts and, if clarification is required, a briefing from the designated forecast unit.

29
Q

What is a Barometer?

A

A barometer is used to pressure gas pressure. 2 types are the Mercury and Aneroid Barometer (the altimeter is an aneroid barometer). A barograph transfers readings onto a graph.

30
Q

What is a Thermometer?

A

Used to measure temperature (dry bulb) or humidity (wet bulb).
If the 2 measurements are close together, this means humidity is high and the air is near saturation. In these conditions fog and low visibility are probable.
Measured by Mercury in glass- expands as temperature increases.
Housed in Stevenson Screen (shelter) 1.5m above the ground.

31
Q

What are the characteristics of the Troposphere?

A
  • Depth of 16km (55,000ft) at the equator to 8km (25,000ft) at the poles.
  • Air temperature and pressure decrease with height.
  • Upper limit know as the tropopause.
  • Generates and contains 99% of earths weather.
32
Q

What are the characteristics of the Stratosphere?

A
  • Lies above the tropopause up to 50km
  • Temperature INCREASES from -51°C to surface values due to solar radiation absorbed by ozone.
  • Relatively stable layer with no strong vertical motion
  • Little or no weather phenomena
  • Upper limit is stratopause.
33
Q

What is the composition of the atmosphere?

A
Nitrogen 78%
Oxygen 21%
Argon 1%
Carbon Dioxide 0.03%
Water Vapour 1-4%
34
Q

What is International Standard Atmosphere, and what is its purpose?

A

The International Standard Atmosphere (ISA) is an atmospheric model of how the pressure, temperature, density and viscosity of the earth’s atmosphere change over a wide range of altitudes.
It has been established to provide a common reference for temperature and pressure and consists of tables of values at various altitudes.
It’s purpose is for the manufacturing and calibration of pressure/speed instruments, the design and testing of aircraft, and as a datum against which deviations can be measured.

Atmospheric Pressure at MSL= 1013.25 hPa
Temperature at MSL= 15°C
Density= 1.225 kg/m^3
Lapse Rate= 1.98°C per 1000ft, up to 11km

35
Q

How is heat transferred?

A

Radiation- energy transmitted by electromagnetic waves (heat from sun).
Conduction- energy passed from one body to another through direct contact.
Convection- mass of air heated, expands and rises, carrying heat energy higher into the atmosphere (main cause of winds and cloud formation)
Advection- as air rises through convection, more air will move in sideways to replace it. This horizontal movement of air brings heat energy and moisture with it.

36
Q

What is Specific Heat Capacity?

A

The amount of energy needed to raise a body of specified mass by 1°C.

37
Q

How is the atmosphere heated?

A
  • Short wave radiation from the Sun absorbed as latent heat. Earth re-radiates long wave terrestrial radiation.
  • Absorption of ultra-violet by the ozone.
  • Scattering by air molecules
  • Reflection by surface (ice especially!) and clouds
  • Latent heat released by condensation.
  • Conduction between air and surface.
  • Long wave radiation absorbed by clouds and water vapour.
38
Q

What are the Phases of water?

A

Condensation: water changes from gas to liquid- caused by cooling of air until it can no longer hold the amount of water vapour present.
Evaporation: water changes from liquid to gas.
Sublimation: water changes from ice to gas without passing through liquid state.
Deposition: water changes from gas to ice without passing through liquid state.

39
Q

What is Latent Heat?

A

The heat absorbed or released without change of temperature, involved in a change of state of a substance.
It is:
REQUIRED for evaporation and sublimation, and
RELEASED during condensation and deposition.

40
Q

What is the relationship between Relative Humidity and the Dew Point?

A

Relative Humidity measures the degree of saturation of the air- when is is saturated RH= 100%
The Dew Point is the degree to which the air must be cooled for it to become saturated.

41
Q

What is Saturation?

A

When the air is incapable of holding any more water vapour. Air in the atmosphere is usually unsaturated. Water vapour is added to the air by evaporation until it is saturated.
Warmer air can hold much more water vapour without becoming saturated than colder air.

42
Q

What is the Adiabatic Process?

A

As air rises it cools by approximately 3°C per 1000ft, known as the Dry Adiabatic Lapse Rate (DALR). Eventually it will reach its saturation point and water vapour will begin to condense and form clouds. As this process occurs energy will be lost in transformation, and as the air continues to rise it will continue to cool but at a slower rate- 1.5°C per 1000ft, known as the Saturated Adiabatic Lapse Rate (SALR).

43
Q

What is the relationship between pressure, temperature and density?

A

Density= pressure/temperature.

As density increases- pressure increases.

As density decreases- temperature increases.

44
Q

What difficult conditions can be associated with clouds?

A

Obscure earths surface features.
Turbulence
Icing
Hazardous for taking off and landing.

45
Q

What is the difference between stable and unstable air?

A

A parcel of air that is warmer than its surroundings will continue to rise. This is unstable.
A parcel of air that tends to return to its original level is stable.

46
Q

How can clouds be formed?

A

Convection- due to heating. Hot air rises and cools, dew point reached and water vapour condenses. Occurs mostly over open land areas.

Frontal/Mass ascent- warm air meets colder air and is forced up slowly. Clouds form over a long front, mainly stratus types. Continuos rain or snow is likely.

Turbulence and Mixing- Prevailing wind blows over broken ground, warm and cold air mixed, clouds formed.

Mountain/Standing Waves- airflow rises and cools over mountainous ground, lenticular clouds formed, strong down drafts and turbulence occurs on lee side. Rotor clouds also formed, often miles away as airflow continues to oscillate. Unstable air could form cumulus or Cb clouds, stable air could form lenticularis, stratus or stratocumulus.

47
Q

What are the four main types of cloud?

A

Cumulus, Stratus, Cirrus and Nimbus.

48
Q

What is Virga?

A

Rating that falls from a cloud but returns to vapour before reaching the ground.

49
Q

What clouds can be found at different heights?

A

High clouds-
20,000- 45,000ft: Cirrus, Cirrostratus, Cirrocumulus.

Medium clouds-
6,500ft-20,000ft: Altocumulus, Altostratus.

Low clouds-
Surface-6,500ft: Nimbostratus, Cumulus, Cumulonimbus, Stratus, Stratocumulus.

50
Q

How are clouds measured?

A

Amount:
Measured in the number of eighths obscuring the sky at that level as viewed from aerodrome level. (In Oktas)

Height:
Base of cloud measured or estimated above aerodrome level by:
- Ceilometer
- Timed balloon ascent
- Pilot reports
- Visual estimation
51
Q

What is the difference between Cloud Base and Cloud Ceiling?

A

Cloud Base- Height of the base of the lowest cloud visible of any amount.

Cloud Ceiling- Height of the base of the lowest cloud visible that covers more than half of the sky.

52
Q

How is cloud cover reported?

A
SKC- Sky Clear- 0 Oktas
FEW- Few- 1 or 2 Oktas
SCT- Scattered- 3 or 4 Oktas
BKN- Broken- 5 to 7 Oktas
OVC- Overcast- 8 Oktas
NSC- No Significant Cloud- No cloud below 5000ft, or Cb or TCu. 

A maximum of 3 layers reported, limited to cloud bases not more than 5000ft above aerodrome level:

  • the lowest individual layer of any amount
  • next highest layer of at least 3 oktas
  • next highest layer of at least 5 oktas

Plus any significant convective cloud, ie Cb/TCu always reported.

53
Q

How is precipitation formed?

A

Condensation in cloud or fog.
Water vapour condenses onto minute particles in the air (duty or smoke)(0.02mm)
Collision and Coalescence, drops grow to 2mm.

54
Q

What is super cooling of water, when might it be a problem?

A

Water droplets cooled below freezing point- don’t freeze due to severe curvature of surface.
Come into contact with flat surface they freeze.

This could be an aircraft wing, icing leads to a change in wing profile which can lead to increased drag and decreased lift.

55
Q

What is the Bergeron process?

A

In clouds with very low temperatures, water droplets can evaporate into water vapour and change into ice crystals.
These ice crystals have a higher fall speed and grow by accretion with water droplets (which freeze on impact) and amalgamation to form snow.

56
Q

Which cloud types produce what type of precipitation?

A

Drizzle- very small water droplets, usually light but can be intermittent or continuos. From: Stratus (St) or Stratocumulus (Sc).

Rain- water droplets larger than drizzle.
From:
Thicker St or Sc or Altocumulus (Ac)- light, intermittent or continuous.
Cumulus (Cu) or Cumulonimbus (Cb)- showers with rapid fluctuations of intensity.
Nimbostratus (Ns)- often heavy and continuos.

Snow/Ice crystals
From:
Ns or Sc in winter (cloud deep enough to penetrate well above 0°C isotherm).
Only reaches the surface if the temperature is below 4°C.

Hail- ice droplets formed by crystals and supercooled water droplets colliding and coalescing.
From:
Cb cloud of great vertical extent. Also needs high liquid content, vigorous up and down draughts and sub-zero temperatures.
Indicative of very unstable air.

57
Q

What types of solids can be in the atmosphere?

A

Sand, Dust, Haze, Smoke, Volcanic Ash, Dust and Sand storms.

58
Q

What is Prevailing Visibility?

A

The visibility value that is reached or exceeded within at least half of the horizontal circle or within at least head of the surface of the aerodrome. These areas could compromise contiguous or non-contiguous sectors.

59
Q

What is the definition of Visibility for aeronautical purposes?

A

The greatest distance at which a black object of suitable dimensions, situated near the ground, can be seen and recognised when observed against a bright background, or

The greatest distance at which lights in the vicinity of 1000 candelas can be seen and recognised against an unlit background.

60
Q

How is Met. Visibility reported?

A

Prevailing visibility always reported.
In addition:
With a general direction if the visibility is less than 1500m or less than 50% of the prevailing visibility.
The most operationally significant visibility (eg runway direction) is reported if the lowest visibility is observed in more than one direction.

When vis is fluctuating rapidly and prevailing vis cannot be determined, only lowest vis should be reported with no indication of direction.
RVR included in METAR whenever lowest vis is less than 1500m.
Present Weather (Smoke, mist, haze) included if vis 5000m or less, or 1000m or less of fog or freezing fog, or fog patches.

61
Q

What is Runway Visual Range (RVR) and Instrumented RVR (IRVR)?

A

RVR- Indicated the range over which the pilot on the centreline of the runway can expect to see the runway surface markings, and the lights delineating the runway or identifying its centreline.

IRVR- Automatic and continuous display of RVR values, measured at Touchdown, Mid-Point and Stop End.

62
Q

What conditions must exist for CAVOK (Cloud and Visibility Ok) to be reported?

A
  • Vis 10km or more
  • No Min Vis reported.
  • No cloud below 5000ft or Min Sector Altitude, whichever is greater.
  • No Cb or TCu at any level.
  • No significant weather phenomena in the vicinity of the aerodrome.
63
Q

How are reductions in visibility defined?

A

Fog (FG)- A suspension of small water droplets reducing vis below 1000m
Mist (BR)- Same as fog but vis not less than 1000m
Haze (HZ)- A suspension of solid particles of smoke or dust reducing vis to not less than 1000m when relative humidity is less than 95%.

64
Q

What are the conditions for the formation of Radiation Fog?

A

Clear Sky- earth radiates heat energy
Land Surface- rapidly cools and conducts cooling to adjacent air.
Moist Air- layer in contact with ground reaches dew point.
Light Wind- 2-8kts to provide light turbulence
Long Night- allows max time for effect to establish.

NB Cleared by solar heating, cloud cover, increased winds.

65
Q

What is Advection Fog?

A

Formed when warm, moist air transferred by advection currents to a cold land or sea area.
Warm air loses heat to cold surface and fog forms if this cooling effect is sufficient to saturate the air.

NB Dispersed by change of airmass to drier air, ground heated above dew point of air mass, increased wind.

66
Q

What rules govern the transmission of Met Information to aircraft?

A
  • Any information supplied must conform with pilots request.
  • Only Met Office supplied info to be transmitted, except:
    Indicated wind speed/direction
    RVR observations
    Sudden or unexpected deteriorations
    Info from aircraft in flight (turbulence, wind shear)
    Cloud echoes observed on radar (shouldn’t really!)
    Observations by qualified ATS staff member
    SIGMET messages relayed to all aircraft without delay.
67
Q

What weather might prompt a Met Office Aerodrome Warning?

A
Gales
Strong Wind warnings
Squalls, hail or thunderstorms
Snow
Frost
Fog
Freezing precipitation
68
Q

What is a Significant Met Report (SIGMET)?

A

Prepared and disseminated by the Met Office.

Purpose- to warn pilots of actual or anticipated weather conditions that could affect the safety of aircraft operations.

Phenomena to be reported include: Thunderstorms, Heavy Hail, Tropical Cyclone, Freezing Rain, Severe Turbulence, Severe Icing, Severe Mountain Waves, Heavy Sand/Dust Storm, Volcanic Ash.

Aircraft should be warned of any SIGMET phenomena for the route ahead for up to 500nm or 2 hours flying time. They are valid for 4 hours, exceptionally 6 hours, or 12 hours in the case of volcanic ash and cyclones.

69
Q

What are Shallow and Freezing Fog?

A

Freezing Fog- Temperature below zero, rime ice deposited on surfaces.

Shallow Fog- Less than 2m over land/10m over sea. More than 1000m vis above fog layer.

70
Q

How are ICAO weather information requirements laid down in Annexe 3 and 11?

A

Annexe 3- Pilots need to be informed about met conditions along routes to be flown and at destination aerodrome. The objective of met service outlined is to contribute to the safety, efficiency and regularity of air navigation.

Annexe 11- Contains specifications for Operational Flight Information Service (OFIS) broadcasts, including Automated Terminal Information Service (ATIS) broadcasts. This includes Significant Meteorological (SIGMET) information and information on weather conditions at departure, destination and alternate aerodromes.

71
Q

What information does the Met Office (MWO) supply? (9)

A

-Aerodrome Forecasts (TAF)
-Aerodrome Warnings
-Special Forecasts (Red Arrows display etc.)
-At some aerodromes, warnings of marked temp inversions and Wind Shear Alerting Service.
-SIGMETS
-Forecast Regional Pressure Settings (RPS)
-UK Low Level Weather and Spot Wind charts.
-Main Forecast Weather Chart
-Provides pre-flight briefing service via:
Self briefing pic terminals, AIRMET telephone, METFQX services, Dialmet, Internet, Personal advice of forecaster from appropriate met office.

72
Q

What are Special Aircraft Observations?

A

These should be passed to ATC whenever an aircraft encounters or observes any of the following conditions:

  • Severe Turbulence
  • Severe Icing
  • Severe Mountain Wave
  • Thunderstorms, with or without hail, that are obscured, embedded widespread or in squall lines.
  • Volcanic Ash clouds.

Special Air-Reports including this information should always be passed to other aircraft and the met office at Exeter, and cover up to 1 hour flying time ahead.
They should also include position (Lat and long), time, flight level and the met conditions.

73
Q

What is a METAR, what information does it contain and how often is it promulgated?

A

Aviation routine weather report.
Half hourly or hourly 20 and 50 minutes past the hour (sent over OPMET).
Contains: surface wind (direction, speeds and gusts if over 10kts greater than the mean speed), surface visibility (including direction of reduced visibility area), weather, cloud (up to 3 separate layers), CAVOK, QNH, QFE, air temperature/dew point, any remarks.

74
Q

What is a SPECI and when would it be issued?

A

Special Aerodrome Met Report
Issued whenever a change of specified criteria occurs in:
Wind, visibility, RVR, Weather, Cloud, Temperature, QNH, Severe icing/turbulence.

75
Q

What is a Quasi-stationary front?

A

When a warm front and cold front meet and neither have the power to overcome the other, thus the front remains stationary.

76
Q

What is VOLMET?

A

A means of transmitting met information. METARS and SPECIs plus trend type landing forecasts, and occasional SIGMET information, are transmitted continuously on VHF and repeated at 30 minute intervals on HF.

77
Q

What is ATIS?

A

Automatic Terminal Information System- A repetitive recording that is continuously transmitted on a dedicated airfield VHF frequency. It transmits, in plain language, aerodrome status, current weather and the information code (each consecutive ATIS message is coded with A, B, C etc. to enable confirmation that a pilot has the most recent information).
With each departure ATIS the controller should obtain a read back of relevant pressure settings.

78
Q

What is SAMOS and ADIS?

A

Semi Automated Meteorological Observing System (at most NATS airports).
Automated Data Information System.

Both displays of meteorological data at radar stations to assist controllers.